North American owls range in size from the tiny elf owl—at 5¾ inches, the world’s smallest owl species—to the great horned owl, a powerful predator that is nearly 2 feet long. Ecologically, owls are similar to hawks but hunt at night rather than during the day. Both owls and hawks have plumage that is primarily brown, rust, black and white. Differences stem from owls’ nocturnal hunting. The birds have round facial discs, for instance, that focus sound waves to highly sensitive ear openings. And owls’ eyes are specially adapted to gather what little light may be available at night.